The present invention relates to thermoplastic elastomers resulting from the dynamic vulcanization of a compatibilized blend of an aromatic polyester and an epoxy or ortho ester functionalized EPDM rubber. More particularly, the present invention relates to products obtained by the melt extrusion of blends having an effective amount of a free radical initiator, and a compatibilized blend of an epoxy or ortho ester functionalized ethylene-propylene-polyene terpolymer (EPDM rubber) and and aromatic polyester, such as polybutylene terephthalate (PBT).
Prior to the present invention, thermoplastic elastomers were developed to provide materials which could be processed as thermoplastics and yet have the ability to retract forcibly from a large deformation. A term often associated with thermoplastic elastomer is "dynamic vulcanization" which is described by A. Y. Coran et al, Rubber-Thermoplastic Compositions, Rubber Chem Technology 55 (1982) 116. More details about dynamic vulcanization is shown by Coran, in Thermoplastic Elastomers, A Comprehensive Review, edited by R. N. Legge et al on pages 135-156, MacMillan Publishing Company, New York, 1987. In dynamic vulcanization, an elastomer, such as an EPDM rubber, i.e. an ethylene-propylene-diene monomer rubber is vulcanized during its melt-mixing with molten plastic. Although dynamic vulcanization can provide compositions which are very elastomeric in their performance characteristics, it has been found that when the EPDM rubber is dynamically vulcanized during melt mixing with a thermoplastic material, it is often difficult to produce a finely dispersed blend of EPDM and the thermoplastic material at the desired blend ratios of interest. Improved compatibility between thermoplastic resins, such as, PBT and EPDM rubbers has been achieved by modifying the EPDM rubbers with an ester of an .alpha.,.beta.-unsaturated acid having an epoxide functional group on the alkoxy portion, such as, glycidyl methacrylate, as shown by European patent application 0,274,744 or by modifying the EPDM rubber with an ortho ester as shown in copending application Ser. No. 07/645,177. Additional uses of EPDM rubbers modified with an epoxy functional ester of an .alpha.,.beta.-unsaturated acid are as impact modifiers for aromatic polyesters, as shown by European patent 0,309,800.
Although the proportions of the EPDM rubber and plastic components have been found to have an effect on physical properties, such as tensile strength (psi) and elongation at break (%) it would be desirable to obtain elastomeric thermoplastic compositions having reduced Tensile set (%) as defined hereinafter, or correspondingly enhanced elastic recovery % as well as valuable physical properties, such as tensile strength (psi) and elongation at break (%) resulting from the melt blending of mixtures of aromatic thermoplastic polyesters and EPDM rubbers.